[beat]

Really, it is the modern terminology, despite being over 2000 years old. Western philosophy is built almost entirely on a sequence of ideas dating back to Plato (and ancient Greek philosophy in general). Modern philosophers analyze the key concepts identified by Plato and his peers, whether they agree with Plato (or Aristotle, or Diogenes, or other writers of the era) or not.

Modern philosophers tend to be extremely dense and difficult to read. What I'd recommend is starting from the beginning - key works of Plato, such as Apology (the trial and death of Socrates), Republic (an ideal government, and Symposium (a friendly conversation about the topics of the day). These are all quite readable and enjoyable, and frankly as good as or better than most modern works.